The present invention relates to a liquid crystal display element, a substrate for the liquid crystal display element, a liquid crystal display, a method for fabricating the liquid crystal display element, and a method for driving the liquid crystal display element, which have a display capability of a high-speed response and a wide viewing angle. More particularly, the present invention relates to a liquid crystal display element, a substrate for the liquid crystal display element, a liquid crystal display, a method for fabricating the liquid crystal display element, and a method for driving the liquid crystal display element, which are of an optically self-compensated birefringence mode cell type and facilitate spray to bend transition.
With advance of multimedia technologies, image information has greatly occupied a position in multimedia. In recent years, a liquid crystal display with high contrast and a wide viewing angle has been developed and put to practical use, with development of liquid crystal technologies. Now, the liquid crystal display is equal to a CRT (Cathode Ray Tube) display in performance.
However, in the current liquid crystal display, an image is blurred due to image retention because of a low response speed in display of a moving image. In this respect, the current liquid crystal display is inferior to the CRT display.
In the past, many attempts have been made to provide a high-speed responsive liquid crystal display. While various liquid crystal display systems of the high-speed response are arranged by Wu et al. (C. S. Wu and S. T. Wu, SPIE, 1665, 250 (1992)), a system and method that realizes a response characteristic required for display of a moving image is limited.
Specifically, in the current NTSC (National Television Standard Committee) system, it is required that a liquid crystal follow a video signal in one frame (16.7 msec). While the current liquid crystal display has satisfactorily high-speed responsiveness between white and black values, it has responsiveness as slow as not less than 100 msec in a response between gray scales in multiple gray scale display. In particular, the response between gray scales in an area where a driving voltage is low is noticeably slow.
Currently, as potential liquid crystal displays having high-speed responsiveness suitable for display of the moving image, there are an OCB (Optically Compensated Birefringence) mode liquid crystal display element, a ferroelectric liquid crystal display element, and an antiferroelectric liquid crystal display element.
In actuality, however, the ferroelectric liquid crystal display element and the antiferroelectric liquid crystal display element having a layer structure have many problems associated with their practical use: low shock resistance, a limited range of available temperatures, high temperature dependency of property, and so forth. Hence, the OCB mode liquid crystal display element using a nematic liquid crystal is considered to be promising as the liquid crystal display element suitable for display of the moving image.
The OCB mode liquid crystal display element is a display system, the responsiveness of which was demonstrated by J. P. Bos in 1983. Thereafter, it was demonstrated that combination of the OCB mode liquid crystal display element and a film retardation film brought about a display with a wider viewing angle and a high-speed responsiveness, and the OCB mode liquid crystal display element has been studied and developed actively.
Referring to FIG. 14, the OCB mode liquid crystal display element comprises a glass substrate 1 on which a transparent electrode 2 is formed, a glass substrate 8 on which a transparent electrode 7 is formed, and a liquid crystal layer 4 disposed between the substrates 1 and 8. Alignment layers 3, 6 are formed on the electrodes 2 and 7, respectively, and have been subjected to alignment treatment to orient liquid crystal molecules in parallel with one another and in the same direction. Polarizers 13 and 16 are provided in cross nicol on the outsides of the substrates 1 and 8, respectively. A retardation film 17 is interposed between the polarizer 13 and the substrate 1 and a retardation film 18 is interposed between the polarizer 16 and the substrate 8.
A liquid crystal cell so structured is characterized in that bend orientation or bend orientation including twist orientation is induced in a central portion of the cell by application of a voltage and the retardation films 17 and 18 are provided for driving a low voltage and enlarging a viewing angle. The cell has a capability of a high-speed response in a medium gray scale display area and a wide viewing angle characteristic.
In a normal state, the OCB mode liquid crystal display element is operated at a voltage at which a liquid crystal in a liquid crystal panel maintain the bend orientation. Below a given voltage, since the spray orientation state is more stable than the bend orientation state, transition to the spray orientation takes place. This transition is irreversible. A pixel with the spray orientation is thereafter left on the liquid crystal display element as a display defect (luminescent spot), which impedes its normal display operation.
In the OCB mode, an initialization process for transitioning from an initial spray orientation state 4a to a bend orientation state 4b by application of a voltage is essential.
However, the application of the voltage at approximately several volts requires some minutes for the initialization process, which is one of the problems with the OCB mode. Accordingly, there is a need for a liquid crystal display element with a high transition speed in which the bend orientation is easily formed by applying a voltage at several volts.
Japanese Patent Application Publication No. 11-7018 discloses techniques for high-speed transition from the spray orientation to the bend orientation (hereinafter referred to as xe2x80x9cspray to bend transitionxe2x80x9d) in the OCB liquid crystal display mode. The techniques are a technique for adding a chiral agent to a liquid crystal, a technique for uniformly forming twist over the entire surface of a liquid crystal panel at an angle of 180 degrees, and a technique for uniformly forming twist over the entire surface of the liquid crystal panel at an angle of 10 degrees. However, these techniques are not useful in achieving the high-speed spray to bend transition. When the spray to bend transition unreliably takes place and thereby an area of the spray orientation is locally left, the area becomes a luminescent spot, which looks like a spot defect.
The present invention is directed to solving aforesaid problems and an object of the present invention is to provide a liquid crystal display element, a substrate for the liquid crystal display element, a liquid crystal display, a method for fabricating the liquid crystal display element, and a method for driving the liquid crystal display element, which are capable of high-speed and reliable transition of spray orientation to bend orientation.
To solve the aforesaid problem, the inventors observed the behavior of the spray to bend transition. The observation result is that a nucleus of the bend orientation is generated from a specific portion and is grown. After intensive study, the inventors discovered that a twist orientation locally formed becomes a nucleus, from which bend transition occurs.
A first aspect of the present invention is based on this knowledge. According to a first aspect of the present invention, there is provided a liquid crystal display element comprising at least one substrate and a liquid crystal layer, wherein a different orientation direction area of an orientation direction locally different from an orientation direction of the other area is present on the liquid crystal layer. More specifically, the liquid crystal display element comprises a pair of substrates and a liquid crystal layer, wherein the pair of substrates have been subjected to substantially parallel alignment treatment and a different orientation direction area of an orientation direction locally different from an orientation direction of the other area is present on the liquid crystal layer.
With such a configuration, since the nucleus of the bend orientation is generated from the different orientation direction area by utilizing a nematic liquid crystal and is grown, causing the spray to bend transition to occur, high-speed and reliable spray to bend transition becomes possible. The substrate as defined herein refers to a plate-shaped member having an inner surface contact with a liquid crystal layer in a constructed liquid crystal display element, including an upper substrate, a lower substrate, a color filter substrate, a TFT substrate, and the like.
The different orientation direction area may be stationary or nonstationary. The nonstationary different orientation direction area includes an area having a transient orientation state or an orientation state formed by the lateral electric field.
The stationary different orientation direction area is formed by an orientation capability of the member contact with the liquid crystal with respect to the liquid crystal molecules. The orientation capability is realized by alignment treatment performed on the member contact with the liquid crystal and the orientation capability of the member with respect to the liquid crystal molecules.
As the alignment treatment performed on the member contact with the liquid crystal, rubbing, a photo-alignment treatment, formation of grooves on the surface of the member, and formation of a scratch on the surface of the substrate can be employed.
As the orientation capability of the member contact with the liquid crystal with respect to the liquid crystal molecules, water-repellency and hydrophilicity of a material of which the member is made, and a shape of the member may be employed.
The rubbing treatment is performed in a variety of manners A second aspect of the present invention is preferred manners of the rubbing treatment. In the liquid crystal display element according to the second aspect of the present invention, at least one substrate has been subjected to alignment treatment such that a different orientation direction area of an orientation direction locally different from an orientation direction of the other area is present in the liquid crystal layer and the alignment treatment is a rubbing treatment.
To form the different orientation direction area by rubbing, the steric obstacle is formed on the inner surface of the substrate and rubbing is performed on the substrate having the steric obstacle. Thereby, rubbing is controlled by the steric obstacle to thereby form the area subjected to alignment treatment differently from the other area around the steric obstacle on the inner surface of the substrate. The portion of the liquid crystal situated on the area becomes the different orientation direction area.
The steric obstacle has a shape to control rubbing, including a column-shaped body, a cone-shaped body, or a convex body.
The steric obstacle may be a complex body constituted by a plurality of steric obstacles formed as being contact with each other. With such a configuration, a portion where the different orientation direction areas are contact with each other is generated and functions as a nucleus of transition. Consequently, higher-speed and more reliable spray to bend transition is achieved.
The steric obstacle serves as the column spacer. With such a structure, the column spacers can be saved.
Next, the inventors found the following knowledge. When the applied voltage is set to zero volt momently after transition of the liquid crystal to the bend orientation, the liquid crystal is transformed into twist orientation of 180 degrees. When the voltage is applied again while the twist orientation of 180 degrees remains, the liquid crystal transitions to the bend orientation in a very short time and at an extremely low voltage.
A third aspect of the present invention is based on the above knowledge. According to the third aspect of the present invention, there is provided a liquid crystal display element comprising a liquid crystal that is in a first orientation state under a no-voltage condition and in a second orientation state under a display voltage and has an energy barrier between the first and second orientation states and voltage application means for applying a voltage to the liquid crystal, wherein the liquid crystal partially includes an area in a third orientation state in which an energy barrier existing between the second and third orientation states is smaller than an energy barrier existing between the first and second orientation states under the no-voltage condition. With such a configuration, since the area in the third orientation state becomes transition nucleus, it is possible to transition the liquid crystal to the second orientation state more quickly, at a lower voltage, and more reliably.
The third orientation state may be a stationary state under the no-voltage condition. This includes the orientation state of the stationary different orientation direction area described in the first aspect.
The aim of the third aspect of the present invention is that the third orientation state is a non-stationary state, i.e., the transient state of transition between the first and second orientation states.
When the transient state is the transient state from the second orientation state to the first orientation state, it is possible to transition the liquid crystal to the second orientation state by far more quickly, at a much lower voltage, and more reliably.
When the transient state is preserved by the incomplete surrounding body, it is possible to appropriately preserve the transient state.
The third orientation state may be at least a portion of the second orientation state preserved under the no-voltage condition. With such a configuration, it is possible to transition the liquid crystal to the second orientation state by far more quickly, at a much lower voltage, and more reliably.
When at least a portion of the second orientation state is preserved by liquid crystal molecule orientation capability of the steric object existing in the liquid crystal or the net structure existing in the liquid crystal, it is possible to appropriately preserve at least a portion of the second orientation state.
A fourth aspect of the present invention is to form the different orientation direction area by a lateral electric field. That is, the fourth aspect is aimed at forming the nonstationary different orientation direction area. According to the fourth aspect of the present invention, there is provided a liquid crystal display element comprising a liquid crystal layer disposed between a pair of opposite substrates wherein a source line, a gate line, and a pixel electrode are formed on one of the substrates and a counter electrode is formed on the other substrate, wherein adjacent edge portions of the pixel electrode and one of the source and gate lines are engaged with each other as having a predetermined gap seen in a plan view. With such a configuration, the lateral electric field is generated in the engaged portion by application of a predetermined voltage to form the different orientation direction area in the liquid crystal layer, thereby facilitating the transition.
The portions engaged with each other may be zigzag-shaped. With such a configuration, two twist-oriented areas in opposite directions and contact with each other are formed in the liquid crystal layer by the lateral electric field formed in the zigzag-shaped portion, thereby enabling quick and reliable bend transition.
The potions engaged with each other may be convex. With such a configuration, by suitably selecting the rubbing direction, the twist-oriented area having a larger twist angle is formed in the liquid crystal layer by the lateral electric field formed in the convex portion, thereby enabling the high-speed and reliable bend transition.
In this case, it is preferable that the lateral electric field formed in the convex portion has an intersection angle of 45 to 135 degrees with respect to a direction of a parallel alignment treatment performed on the pair of substrates.
This object, as well as other objects, features and advantages of the invention will become more apparent to those skilled in the art from the following description taken with reference to the accompanying drawings.